Bug#26585560 - MYSQL DAEMON SHOULD CREATE ITS PID FILE AS

ROOT

DESCRIPTION
===========
If the .pid file is created at a world-writable location,
it can be compromised by replacing the server's pid with
another running server's (or some other non-mysql process)
PID causing abnormal behaviour.

ANALYSIS
========
In such a case, user should be warned that .pid file is
being created at a world-writable location.

FIX
===
A new function is_file_or_dir_world_writable() is defined
and it is called in create_pid_file() before .pid file
creation. If the location is world-writable, a relevant
warning is thrown.

NOTE
====
1. PID file is always created with permission bit 0664, so
for outside world its read-only.
2. Ignoring the case when permission is denied to get the
dir stats since the .pid file creation would fail anyway in
such a case.

include/sql_common.h

@@ -107,6 +107,7 @@ void mysql_client_plugin_deinit();
 struct st_mysql_client_plugin;
 extern struct st_mysql_client_plugin *mysql_client_builtins[];
 extern my_bool libmysql_cleartext_plugin_enabled;
+int is_file_or_dir_world_writable(const char *filepath);
 
 #ifdef	__cplusplus
 }